Fish farming is an industry growing at a rapid rate, which is driven by the demand for increased quantities of food resources and the decrease of natural sources of fish in lakes and oceans. Fish farming usually involves floating cages, which are positioned just offshore in fjords, seas, lakes or other natural bodies of water. The fish cages are usually wide cages comprising a rigid cylindrical frame structure positioned horizontally on the surface of the body of water and a net system allowing water to flow into and out of the cage. The net system is made with net meshes of sufficiently small size to retain the fish inside the cage. Such conventional cages typically have a circular bottom net, a cylindrical sidewall net extending to the water surface and an open top end, which may also be covered by a net.
In the most common setup for fish farming plants, a number of floating net cages are anchored close to shore using buoys and weights to stabilize the cages in the water. An optimal installation for fish farms of this sort is in sheltered waters such as bays and fjords and these setups often comprise support frames with gangways for operational purposes, such as maintenance and feeding.
Surface cages, however, are sensitive to severe weather conditions, such as high winds, waves and ice, which can be a serious threat in northern areas. Submersible cages have been suggested and tested. However, these types of cages have not become commercially feasible due to problems with stability, handling and cost.
For example, PCT Publication No. WO 82/03152 to Rene and French Patent Application No. 2420920 to kin both describe substantially cylindrical shaped cages that can rotate when in a semi-submerged position. An inherent problem with cylindrical cages having long spans connecting rings is that the structural integrity of the cage often becomes compromised during severe changes in its environment.
Spherical or geodesic shaped cages have also been proposed. For example, PCT Publication No. WO 2006/050386 to Ocean Farm Technologies, Inc., and United States Patent Publication No. 2006/0096548 to Ytterland et al., both describe spherical or geodesic shaped cages.
In some instances, spherical or geodesic shaped cages can better withstand environmental changes. However, it may be more technically challenging to rotate a spherical cage while submerged. The cage described in PCT Publication No. WO 2006/050386 is made of individual triangular net panels. The buoyancy of each panel can be controlled by selectively introducing air and/or water to the panels or a group of panels, thus allowing rotation of the sphere. Depending on the particular net panel that is to be rotated to the top of the cage, mooring lines are manually attached to hubs present at the intersection of adjacent net panels in order to facilitate rotation.
United States Patent Publication No. 2006/0096548 to Ytterland et al., describes another spherical cage that is attached to platform that circumferentially connects opposite ends of a central pole. Motors are provided on the platform at the intersection between the platform and the central pole. The motors allow the cage to be rotated when the platform is resting on the surface of the water. Rotation of the cage while submersed would be difficult, since the platform would have a tendency to rotate instead of the cage, therefore providing no functionality while submerged.
Accordingly, there is a need for a simple, robust, durable and commercially practical cage and system for commercially cultivating marine animals both on the surface and while submerged, which is easy to manufacture and install and can be maintained underwater and readily manipulated to allow for the collection of animals, sorting of animals and maintenance of the cage.